Copper, fiber optic, and plenum cables and conduit exist in large numbers in most commercial buildings. These cables and conduit may meet the limited combustible requirements as defined in standard NFPA 90A (Standard for the Installation of Air Conditioning and Ventilation Systems), which Standard requires that such cables when tested by standard NFPA-259 have a potential heat value (“PHV”) below 3500 BTU/pound and when tested by NFPA-255 have a smoke developed index (“SDI”) below 50 and a flame developed index (“FDI”) below 25. Such limited combustible cables (“LC Cables”) are also referred to in industry as Duct Cables, CMD, 25/50/8, 25/50, CMP-50 Cables and/or by other references indicating compliance with the PHV, SDI and FDI requirements referenced in the NFPA 90A Standard for limited combustible materials.
The LC Cable constructions are generally referred to as either copper (electrical) or fiber (fiber optic) cable constructions. Typical cable constructions are taught, for example, in U.S. Pat. No. 4,804,702. The components of a cable may include a jacket, primary insulation, a shield tape, and may include various sub-components such as a strength member, film, buffer, separator, pull cord, sub-jacket, all well known in the industry, any one or more of which may be made of a fluoropolymer resin like PVDF.
When cables are replaced, generally the old cable is left in place, and new cable run beside the abandoned cable. As the quantity of cable, both used and abandoned increases, the potential fire and smoke danger presented by these cables also increases. More stringent standards are being proposed to address the fire and smoke danger created by the large systems of cable.
To date, all LC Cables have been developed with fluorinated ethylene propylene (“FEP”) resins for both their primary insulation and jacket components. PVDF has a potential heat ranging between 5700 and 6500 btu/lb, and inherently does not meet the limited combustible requirements for potential heat. PVDF has historically been limited to applications where its poor dielectric properties do not interfere with the performance of a cable. It has been understood in the industry that PVDF compounds with high limited oxygen index (“LOI”) values would be useful for plenum grade cables. Such high LOI compositions are taught, for example, by U.S. Pat. Nos. 4,898,906 and 5,919,852.
U.S. patent application Ser. No. 10/755,504, describes SDI and/or FDI values when one or more of the FEP cable components (such as the jacket or primary insulation) are replaced by PVDF-based components, provided that the cable contains no more than about 50 weight % PVDF, based on the weight of the cable. In a preferred embodiment, one or more of the LC cable components are comprised of PVDF and from about 0.02 to about 2.0 weight % (more typically from about 0.05 to about 1.0 weight %), based on the weight of the PVDF, of a flame, smoke suppressant or char former such as one or more of a tungstate, molybdate or silicate.
Some inorganic fillers reduce the onset temperature of degradation such as the silicates, tungstates, and molybdates. Other fillers acted as acid scavengers such as zinc oxide and calcium carbonate and increased the onset temperature of degradation. In all cases, the addition of these fillers had some negative impact on heat release rate and/or smoke generation. These fillers in general react with effluent gasses produced by combustion of PVDF (such as HF), effecting the burning characteristics of the compound. Therefore, fillers are generally not used in PVDF.
Surprisingly it was found that inorganic fluorides, such as calcium fluoride, can be used as a non-reactive filler in PVDF, associated copolymers and other fluoropolymers. The inorganic fluorides can therefore be added indiscriminately to obtain a number of useful properties. The addition of fillers in fluoropolymers have multiple applications beyond that of limited combustible and plenum products including but not limited to increasing flexural modulus, increasing hardness, reducing coefficient of friction, reducing coefficient of thermal expansion, improving chemical and permeation resistance, reducing smoke generation, improving char forming characteristics, reducing the dielectric constant, and also acting as a low/moderate cost polymer extender.